We recently learned the sad news that Dr. Akira Tonomura – a truly great experimentalist – passed away on May 2, 2012 during the course of treatment on pancreatic cancer.

We have been great admirers of Dr. Tonomura. Our blog’s banner is a cartoon representation of an experimental setup developed by Dr. Tonomura, through which in 1986 he showed single-electron buildups of electron wave interference fringe patterns. This experiment clearly revealed the dual nature of electrons and was described by Physics World magazine as the world’s most beautiful physics experiment, ranking above the historical experiments of Galileo Galilei and Robert Millikan.

This figure from our book “Exploring Quantum Physics Through Hands-On Projects” shows a schematic representation of the modifications that Tonomura made to a transmission electron microscope to develop his experimental setup. Electrons are emitted from a very sharp tungsten tip by applying a potential difference of 3 to 5kV between the tip and a first anode ring through an effect known as “field emission.” These electrons are then accelerated to the second anode potential of 50kV (the de Broglie wavelength for the accelerated electrons is λ=0.0055nm). Assorted “electron optics” within the modified electron microscope attenuate and focus the electron beam so that a current of barely 1,000 electrons per second is beamed towards the double-slit.

The double-slit is actually an extremely fine wire filament (1μm diameter) placed between two conductive plates a centimeter apart. The wire is biased at a positive voltage of 10V relative to the plates. This arrangement is known as an electron biprism.

Obviously, any electrons that make it past the biprism must have gone either through one or the other side of the fine wire. Two electron lenses then magnify the interference pattern 2,000 times and project it onto a fluorescent screen. Each 50keV electron hitting the screen produces about 500 photons which generate photoelectrons inside an intensified position detector. A computer then integrates the hits to produce a final image of the electron interference pattern. Through which slit did each of the electrons go? The answer is that somehow each electron goes through both slits at the same time!

Another one of Dr. Tonomura’s major accomplishments was his experimental verification of the Aharonov–Bohm (AB) effect. For this experiment, Dr. Tonomura used electron holography. Tonomura fabricated a tiny toroidal ferro magnet covered with a layer of superconducting niobium to perfectly shield the magnetic field. His group then measured a phase difference between the electrons that traveled through the central hole of the toroid and those outside it. Although the electrons had only progressed through regions free of electromagnetic fields, there was an observable effect produced by the existence of vector potentials, and thus verifying the AB effect.

We are deeply saddened for the untimely death of such a great scientist.

When we are looking to find a proof of a theory, we tend to disregard other possible explanations if the results seemed to confirm the theory.

In this experiment, the electrons did not go through 2 fine slits. A fine wire was placed in their path. When an electron goes far enough from the wire, it goes strait to the screen below.

Because the wire is positive 10 volts, if the electron passes closer to the wire, it is force to go close to the wire. Some electrons touch the wire and do not go further. Some electrons passes near the wire and their path is bent a little before going to the screen. We have to remember that the surface of the wire is made only of electrons also. The electrons of the wire have a specific velocity and all the values are not possible. We say that these values are quantized, meaning they jump from on value to the other. That is why when a moving electron gets close to the wire, it will experience a force that is also quantized. That is why the screen will show regions where more electrons fall and regions where less electrons fall. They do not go through both side of the wire and they did not interfere with themselves because they are not an kind of electric wave. They are complex systems that can be produced simply by passing a high frequency light through a thin metal sheet.

Another experiment with 2 real slit was performed and can be seen at https://courses.physics.ucsd.edu/2017/Spring/physics142/Lectures/Lecture3/DoubleSlitExperiment.pdf

The results gave this picture:

They are similar to the former picture. But since the side of the slits is made of atoms and the electrons of these atoms have energy not in continuous form but as a multiple of h also, it is normal that single electrons passing through the slit gets a certain energy that is a multiple of h also. That is enough to explain the dark regions where less electrons activate the sensors. It does not necessarily means that a single electron passed though both slit as a wave and recombined as a particle when hitting the sensors.